Questions And Answers

A cohort purchased several "wireless" ESD wrists straps for his PC maintenance bench. He was told they worked similar to a corona wire on a copier/laser printer. I thought it may be a part of a composite system, but he said the need for other equipment was not mentioned. He is now convinced it does not work by itself as he was shocked while opening his car door (while wearing the strap). There is a small oblong monolith attached to the cloth-elastic strap, which a brass colored screw is screwed into. The head of the screw is exposed. I carefully opened one with a dremmel tool and found a 1M resistor wired between a second screw which contacts the wrist contact-plate and a soft rubbery "C" shaped plate (about 1 mm thick, 2 cm sq with a chunk removed forming this c-shape) which the brass colored screw contacts. Does this sound like anything viable? - Anonymous, S. Portland, ME

Answer

No. This is not a viable ESD control device to employ in ESD safe areas. These passive "wireless" wrist straps have severe limitations. Assuming you were tribocharged to 10 KV and wearing the "wireless" wrist strap, it would take many hours (days even depending on the ambient RH) to get you below 5 KV, never the less 10 Volts. Most (if not all) of the charge reduction would be due to natural recombination of the charges on your skin (and now metal casing of your "wireless" wrist strap) with the air molecules and the natural conductance of the air through water vapor content (RH).

P.S. You could get the same effect by cutting your hair to about 1/4" long and then putting conductive jell in your hair. The ends of your now conductive hair would act like corona discharge points at extremely high voltages to bleed current into the air or help to enhance the natural recombination process. The fact that your hair would need to come in very close proximity [0.1 to 1.5 inches] to ground or any other potential with at least a 3 Kilovolt difference (due to the dielectric strength of air) or enhancing the natural conductivity of the air needs to be considered to even get you down below a few KV.